This invention is in the field of drilling bits and particularly bits adapted to be impacted periodically on the formation being drilled.
It has been proposed to provide well drills having drill bits adapted to be periodically impacted against the formation to facilitate drilling. See, for example, the patents to Snyder, U.S. Pat. No. 2,742,685, Stilley, U.S. Pat. No. 2,400,853 and Grant et al, U.S. Pat. No. 1,748,341. The Grant patent lifts drill bits or chisels periodically, then releases them to the action of springs to effect impacting the formation while in Synder a hammer periodically strikes the drill. In Grant and Snyder rotation of the drill string causes relative rotation between cam elements to effect vertical impaction. In the Stilley patent, a turbine, driven by drilling mud, is caused to drive cams to impact the chisels downwardly, although they are lifted by means of springs.